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PL. Tyack and c.w. Clark
right balance between the need to protect marine mammal populations and
the needs of human sea-faring activities.
2. The Ecological Milieu for Auditory Problems in
Whales and Dolphins
Most research on audition focuses on mechanisms of hearing. This chapter
adopts the approach of behavioral ecology. Behavioral ecologists do not
limit their study to the proximate causes or mechanisms of behavior, but
they also study the ultimate causes of behavior-why animals might have
evolved a particular proximate mechanism. In order to do this, they must
study the current functions of a behavior-how the behavior assists an
animal in survival and reproduction. Sound production and perception are
important components of an animal's communication and sensory system.
The basic functions of sound production and reception are similar for terrestrial animals and cetaceans. Sounds produced or perceived by the animal
are used to:
• Detect predators
• Detect prey
• Orient in, navigate through, and explore the physical environment
• Detect and decode the calls of conspecifics
The evolution of systems for auditory perception and vocal production has
been influenced by the physical mechanisms of sound propagation and
ambient noise in the animal's environment. We will briefly review how the
physics of underwater sound may affect the optimal frequency for acoustic
signals operating over different ranges, discuss noise and masking, and then
discuss from an ecological perspective each of these ways animals may use
sound.
2.1 Absorption of Sound in the Ocean
As discussed in the Introduction, one of the unique properties of underwater sound in the ocean is that low-frequency sound can travel for great distances. Sound is a very effective form of energy for sensing distant signals in
the marine environment. The sea not only offers opportunities for longrange communication, but also for using sound to explore the environment.
The critical factor that favors low-frequency sound is the absorption of
sound energy when it is converted to heat. For each unit of distance sound
travels through water, there is a constant rate of absorption. This constant is strongly affected by the frequency of the sound, as illustrated in
Table 4.1. Absorption can significantly limit the range of higher frequencies,
particularly above 40 kHz or so, where the loss is more than 1 dB/100 m. This
PL. Tyack and c.w. Clark
right balance between the need to protect marine mammal populations and
the needs of human sea-faring activities.
2. The Ecological Milieu for Auditory Problems in
Whales and Dolphins
Most research on audition focuses on mechanisms of hearing. This chapter
adopts the approach of behavioral ecology. Behavioral ecologists do not
limit their study to the proximate causes or mechanisms of behavior, but
they also study the ultimate causes of behavior-why animals might have
evolved a particular proximate mechanism. In order to do this, they must
study the current functions of a behavior-how the behavior assists an
animal in survival and reproduction. Sound production and perception are
important components of an animal's communication and sensory system.
The basic functions of sound production and reception are similar for terrestrial animals and cetaceans. Sounds produced or perceived by the animal
are used to:
• Detect predators
• Detect prey
• Orient in, navigate through, and explore the physical environment
• Detect and decode the calls of conspecifics
The evolution of systems for auditory perception and vocal production has
been influenced by the physical mechanisms of sound propagation and
ambient noise in the animal's environment. We will briefly review how the
physics of underwater sound may affect the optimal frequency for acoustic
signals operating over different ranges, discuss noise and masking, and then
discuss from an ecological perspective each of these ways animals may use
sound.
2.1 Absorption of Sound in the Ocean
As discussed in the Introduction, one of the unique properties of underwater sound in the ocean is that low-frequency sound can travel for great distances. Sound is a very effective form of energy for sensing distant signals in
the marine environment. The sea not only offers opportunities for longrange communication, but also for using sound to explore the environment.
The critical factor that favors low-frequency sound is the absorption of
sound energy when it is converted to heat. For each unit of distance sound
travels through water, there is a constant rate of absorption. This constant is strongly affected by the frequency of the sound, as illustrated in
Table 4.1. Absorption can significantly limit the range of higher frequencies,
particularly above 40 kHz or so, where the loss is more than 1 dB/100 m. This